Drying oil polymer containing an acidic phosphorus compound



United States Patent DRYING 03L POLYMER CQNTAINING AN ACEDIC PHOSPHORUS CGMPGUND Thomas L. Canrfrfi and Alfred E. Balocca, Wheaten, 122., assignors to American Can Company, New York, N. Y., a corporation of New Jersey No Drawing. Application July 9, H54 Serial No. 442,428

6 Claims. (Ci. ree -28s The present invention relates to a novel, economical and effective coating composition. More particularly the present invention pertains to a modified diolet'in polymer coating composition for sheet metal, and especially containers fabricated from ferrous metal sheets.

The use of organic coatings on sheet metal as a protection therefor is old and well known. However due to certain special problems in can manufacture, relatively few of the known coating compositions are applicable to can making. The maximum thickness of the coating on metal cans is but a fraction of the usual thickness of the coatings on other metal surfaces. This extremely thin coating must be hard so as to resist marring during abuse in fabrication and handling of the cans; it must be flexible in order to form a continuous adherent film over can parts that have been fabricated by drawing or bending; and it must be substantially impervious to chemical attack. In relation to the last requirement such a variety of products are packed in cans, each presenting its own corrosive problem, that heretofore there has been no single organic coating composition that is effective against the different types of chemical attack. Therefore it is necessary to develop and use a different coating to resist each particular type of corrosion. Obviously such an operation is costly and troublesome.

During recent years this situation has been aggravated by the tremendous increase in the use of organic coatings over tin coatings. Previously most, if not all, metal containers were made from sheet steel having a protective coating of tin on its surfaces. This involved a tremendous consumption of tin in view of the fact that billions of metal containers are manufactured each year. Due to the growing scarcity of tin and the fact that tin has to be imported from foreign countries such as Malaya, Bolivia and the Belgian Congo, a constant effort has been made by the container manufacturing industry to develop substitute coating compositions and methods whereby to conserve tin or obviate its use entirely. In relation to protective coatings for steel plate, one method of tin conservation has been to reduce drastically the weight of tin deposited on sheet steel and provide supplemental protection by the use of organic coatings thereover. Another method has been to eliminate entirely the use of tin coating and obtain corrosion protection solely by the use of organic coatings.

2,836,508 Patented May 27, 1958 After extensive experimentation with many different materials we have discovered that by modifying a particular diolefin polymer with a small amount of an acidic phosphorus compound and thereafter applying this'novel composition to the surface of a ferrous metal plate and treating the coated plate we could produce a thin, hard, adherent, flexible, heat-stable film thereon which protects the metal substrate from atmospheric and other chemical corrosion and that this film withstood the severe drawing, bending and shaping operations prevailing in sheet metal container manufacture.

Therefore an object of this invention is to provide a substantially universal organic coating for metal containers.

Another object of this invention is to provide a substantially universal organic coating for metal containers that is equivalent in quality and protective value and manufacturing ease to tin coated containers and which is more readily available and less costly than tin.

Another object of this invention is to provide a substantially universal organic coating for ferrous metal containers and many other ferrous products that is more economical and in many respects superior to organic coatings presently and heretofore in use.

A further object of this invention is to provide a substantially universal, tough and flexible organic coating for all types of fabricated sheet metal products which in the course of manufacture have to undergo severe bending, drawing and shaping operations.

Numerous other objects and advantages of the invention will be apparent as it is better understood from the following description which is of a preferred embodiment thereof.

The particular polymer discovered as useful in the present invention is a synthetic drying oil. This drying il is a normally liquid, oily homopolymer of an aliphatic, open chain, conjugated diolefin, particularly butadiene- 1,3. Although it has been found that butadiene-1,3 yields an outstanding drying oil, homologues of butadiene having up to 6 carbon atoms such as isoprene, piperylene and 2,3-dimethyl butadiene-1,3 also yield a satisfactory product. These homologues may be substituted for all or part of the butadiene-1,3 or mixtures of these homologues may be used.

in. the polymerization of the diolefin monomer, boron trifiuoride was found to be the most effective polymerization catalyst. The finished polymer has an average mol ecular weight of about 1600 to 1800 as calculated by the boiling point elevation method, and a relative viscosity of about from 1.15 to'l.25.

Relative viscosity (N is the value of the fraction:

(A) Efliux time of polymer solution (B) Efiiux time of solvent used in polymer solution the procedure, (A) a solution of 350 milligrams of the polymer in 25 cc. of C. 'P. benzene, and (B) a sample of the C. P; benzene used in making the solution of (A)- The determinations are run at 25 C. in a modified st Wald viscosimeter, series 50.

' The above described synthetic drying oil polymer is more fully described in copending application, Serial No.

361,861, ,filed June 15, 1953, Patent No. 2,777,890.

The above described synthetic drying oil polymer without the addition of the acidic phosphorus compound, while showing promise as an organic coating for metal containers is deficient in that regard in many important factors, e. g. blistering, discoloration, adhesion and especially flexibility. This last deficiency results in the assaeos- B, using asthe oil. mentionedin corrosionof. container parts fabricated from plate havinglthe unmodified'polymer asacoating thereon du'e to fracture ofthe coating at'points wherethe substrate metal 'issubje'cted tostressor bending; i

the acidic phosphorus compound inhibiting .oxidative' polymerization of the. cross-linking type during'the curing of thefilm thereby yielding a less brittle," more adherent, and more flexible film. However, since-these theoretical considerationsforin no 'part of the present invention, we. do notwish tobe bound thereby.

' 7 Another surprising and unexpected result obtained by the incorporation ofan acidic phosphorus compound in a drying 'oil film according to the present invention is the marked improvement in the heatstability of the. film. When theiside se'am of a can body is bonded by means of. molten solder having artemperature of 700 F. or

. more,'a great deal ot heat is appliedtoth'e inside coating of the body'adjaceht'the side seam. .This large amount of heat usually causes severeiscorching and discoloration of the coating in thearea' of theside seam and income instances causes this portion; ofthe coating to break down and develop holes. We have found that the coat-' ing compositions .of our invention are remarkably resistant to heat, displayingvery'little scorching or discoloration and no break down whatsoever when subjected tolthe hightemperaturesof the soldering operation.

The term 'acidiciphosphorus compound used herein designates phosphorus acids, phosphorus acid derivatives having at leastone replaceable acidic hydrogen atom and mixtures thereof. 1 Included in the, phosphorus acids are 'ortho-, 'meta-, hypo-, and pyrophosphoric acid, 'phosphorous acids, polyphosphoric acid andlanyrphosphorus compound that will yield a phosphoric acid in aqueous solution; e. g. 1 hydrates of orthophosphoric acid, anhydrous phosphoric acid, phosphorus pentoxide, phosphoric V oxide, phosphoric anhydride, .P2O5' and P 0 ,Of the phosphorus acid derivatives 'we include: inorganic salts of phosphorus .acid such aszinc acid phosphate and ammonium acid phosphate; organic esters of'phosphorus acids such as alkyl phosphates, e.'g. n-amyl phosphate and dibutyl phosphate; and organic salts of phosphorus acids such as' amine phosphates e. g.j mono (dibutyl amine) 'pyrophosphate, dianiline phosphate and dibenzyl 'amine phosphate. Of the acidiephosphoruscompounds disclosed, the unsubstituted phosphorus acids produce superior results and thereforeiarepreferredg. V

In accordance with the invention-the acidic phosphorus the weight of p olymer in the co position, between 0.1% and- 8% of acidic phosphorus compound and preferably between 0.50% and 4.0% is incorporated in the composition. These limits are critical since an amount of acidic phosphorus compound less than the minimum limit fails to give the desired result and an amount thereof greater than the upper limit inhibits curing of the film 'to an excessive degree causing it' to .be soft-and tacky. If the acidic phosphorus compound solution is insoluble in the polymer solution, the addition must be accompanied by vigorous agitation of the mass so that the former is uniformly dispersed throughout the latter yielding a homo-. geneous product. However, with certain acidic phosphorus compounds, e. g. some organic phosphates, a solvent compatible with the synthetic drying oil solution can be used so that a clear solution of acidic phosphorus compound solution in polymer solution can be obtained;

With other acidic phosphorus compounds, it may be ad vantageous to add them as a solid or in the form of a thick slurry. This may be accomplished by milling the acidic phosphorus compound into the polymer.

The time of mixing or temperature of the ingredients is not critical, varying over a wide range. The only limitation as to time of mixing is that'sutlicient time be allowed to insure uniform and intimate'contact of the ingredients. In general 5 015 minutes'should be sutficient.

1 temperature, it is necessary only that. the solutions be respective ingredientstherein.

liquid, i. e. above their'freezing points.

Solvents such as water, lower aliphatic alcohols, 'normally liquid'ketones and combinations thereof can be used as solvents for the acidic phosphorus compounds. Inert organic liquids having a boiling range between 20 C. and 200 C. may be used as solvents for the polymer. Aliphatic hydrocarbonsssuch as solvent naphtha and mineral. spirits, e. g. Varsol (boiling range about C. to 200 C.), Solvesso (boiling range about 95 C. to

,Iri-the coating operation, the. metal sheet may be either spray, dip 'or' roller coated. The procedure generally used in metal container manufacture is theroller coating of flat, metal sheets as by an'apparatus similar to that disclosed in United. States Patent 1,848,856, issued to C. Wagner et al. on March 8, 1932. 'The resin coating is then cured. at an elevated temperature usually by means of a'device similar to that shown and described in United States Patent 1,293,2 61, issued to C. Wagner et al. on February4,-1919. i h f f .In applying the coating ,composition pfthejpresent invention by the froller coa ti g process, the liquid coating composition shouldfhave a viscosityof between.90 and 315 centistokesandpreferably between (and 250 cenitstokes' andv-alsolidsicontent of not ;less,than 20 percent by weight of the total, liquid composition.

In actual"operation the solids content is in -the range V of .40 percent-to dq percent by weight. of the total. To fiqt wa e-rem coat isbaked a a; e p ra of from 375 11?. to420 5F. for: 8 to 15 minutes. "The cured film is approximately from 2.5.x 10-? .to 8.5 X 10" cm. I thick 1 over. .the metal substrate. which corresponds to'atweight"ofapproximately2 mg." perisquareinch to 5 mg. per square inch respectively of; metal plate surface. The following tabulation will serve to illustrate specine; embodimears r thep'resent invention but are in no way intended: as limitations thereonf' each of the renewing exampleslfthe majorconstituent :of the V composition is a 'butadieife polymer asdescribedhereinb efore As to V of solubilities of the Each number represents a difierent composition having that percent by Weight of polymer of the particular acidic phosphorus compound designated.

9 This represents percent by weight of total composition.

Small amounts of other substances may be incorporated into the novel composition of the present invention depending upon the result desired. Included in these are pigments such as aluminum and titanium oxide; waxes as internal lubricants; inhibitors; and vegetable drying oils. A small amount of rubber, natural or synthetic, may be added to imrove the elasticity of the coating.

The data tabulated below shows the superiority of the coating of the present invention over all the other coatings rated on the products shown, thereby illustrating its value as a single replacement for the different coatings generally in use. Table I compares the properties of a coating composition of the present invention, i. e. polybutadiene drying oil modified with 1.0% by weight of drying oil of o-phosphoric acid, to those of the unmodified drying oil and to those of commercial can coatings used in packing corn and pumpkin. The metal substrates used in these tests were CMQ plate (Can Makers Quality uncoated steel sheet), tin plate having low Weight of tin coating per base box of steel (.25 lb.) and tin plate having a high weight of tin coating per base box of steel (1.25 lb.). These coated sheets were then fabricated into container parts and contacted with the products designated below, each coating receiving identical treatment in its contact with the respective products. The coated metal can part was then removed from the product and evaluated, the results of which are shown in the table below. In the numerical ratings given in Table 1, zero is perfect ranging upward therefrom to It is thought that the invention and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes may be made in the matter of the ingredients, their identity and their proportions without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred embodiment thereof.

We claim:

1. A coating composition comprising an oily liquid conjugated diolefin polymer synthetic drying oil formed using a boron trifiuoride polymerization catalyst, and from 0.5% to 4.0% by weight of said drying oil polymer of a phosphorus compound having at least one replaceable acidic hydrogen atom, said diolefin containing 4 to 6 carbon atoms, and said polymer having a molecular weight of about from 1600 to 1800 and a relative viscosity of about from 1.15 to 1.25.

2. A coating composition comprising an oily liquid butadiene-1,3 polymer synthetic drying oil formed using a boron trifiuoride polymerization catalyst, and from 0.5% to 4.0% by weight of said drying oil polymer of a phosphorus compound having at least one replaceable acidic hydrogen atom, said polymer having a molecular weight of about from 1600 to 1800 and a relative viscosity of about from 1.15 to 1.25.

3. A coating composition comprising an oily liquid butadiene-1,3 polymer synthetic drying oil formed using a boron trifiuoride polymerization catalyst, and from unsatisfactory. 0.5 to 4.0% by weight of said drying oil polymer of Table 1 Pumpkin Corn Pork Metal Coating Substrate Process Flexlb. Process Flexib. Process Flexib. Resist. Resist. Resist.

Unmodified polymer 8.9 15. 3 4. 6 11. 6 14. 5 19. 4 Do 4.7 11.7 2.6 5.7 7.0 15.0 Do 3. 3 9.0 2.0 5.6 11.3 11.3 00mm! 00111 coating-m 5. 3 6. 0 6. 3 5. 6 19. 6 10.0 8. 3 6. 3 7. 3 6. 4 24. 7 9. 0 (0 0 9 O 0 0) 5. 1 l0. 4 6. 3 7. 7 6. 0 l0. 3 3.8 6.0 3.3 4.3 8.3 8.0 2.2 5.0 .9 7.0 9.9 12.4

1 Complete failure.

While the novel composition of the present invention has been described specifically as a metal can coating, it has utility of much greater scope. This polymer forms an excellent protective coating on all metal substrates, particularly ferrous metal substrates, where a tough, flexible, adherent, corrosion resistant, heat-stable, continuous film is desired.

a member of the group consisting of an unsubstituted acid of phosphorus, an acid phosphate having at least one replaceable acidic hydrogen atom, an acid phosphite having at least one replaceable acidic hydrogen atom and mixtures thereof, said polymer having a molecular weight of about from 1600 to 1800 and the relative viscosity of about from 1.15 to 1.25.

stituted acid of phosphorus is polyphosphoric acid. A .flQw f l V 5 3 et 31- r 2,836,508 r r v M W V 7 8 4. The composition of claim 3' in which the unsub- References Citedri 'the file of this patent stituted acid of phosphorus is ortho phosphoric'acid. "UNITED'STATES PATENTS M n,

5. The composition of claim 3 in which the: unsube, V sti'tuted acid of phosphorus is phosphorous acid. f}; f I 2340981 j "f- {29,51941 6. The composition of claim 3 in which the unsllb- 5- 2587477 Hunter 1952' 1111 1 92 1221 Sept, 15, 1953.. J;1i1.'12,'1954' 

1. A COATING COMPOSITION COMPRISING AN OILY LIQUID CONJUGATED DIOLEFIN POLYMER SYNTHETIC DRYING OIL FORMED USING A BORON TRIFLUORIDE POLYMERIZATION CATALYST, AND FROM 0.5% TO 4.0% BY WEIGHT OF SAID DRYING OIL POLYMER OF A PHOSPHORUS COMPOUND HAVING AT LEAST ONE REPLACEABLE ACIDIC HYDROGEN ATOM, SAID DIOLEFIN CONTAINING 4 TO 6 CARBON ATOMS, AND SAID POLYMER HAVING A MOLECULAR WEIGHT OF ABOUT FROM 1600 TO 1800 AND A RELATIVE VISCOSITY OF ABOUT FROM 1.15 TO 1.25. 